Heat and radio frequency-curable two-pack soy protein-based polyurethane adhesive compositions

ABSTRACT

An adhesive suitable for bonding wood is both heat curable and radio frequency (RF) curable. This adhesive is composed of an isocyanate-terminated prepolymer and hydrolyzed soy protein having a pH of at least about 9 and advantageously from about 9 to 11.5. The weight ratio of prepolymer to soy protein hydrolyzate ranges from about 70:30 to 90:10.

CROSS-REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

The present invention generally relates to adhesives for joining woodproducts, and more particularly to two-part polyurethane adhesivesmodified with soy protein which adhesives are both heat and radiofrequency (RF) curable.

Glued wood products have been traditionally used in this country in avariety of applications. The adhesives for such bonded or laminated woodproducts conventionally are based on phenol-formaldehyde,urea-formaldehyde, polyvinyl acetate, resorcinol-formaldehyde, polymericdiphenylmethane diisocyanate (MDI), and hot met adhesives. The gluedwood products include plywood, particleboard, oriented strand board(OSB), medium density fiberboard (MDF), laminated veneer lumber (LVL),laminated beams, and a variety of other engineered wood products. Amongthem, laminated beams, I-beams, LVL, and a variety of engineered woodproducts are used for structural wood applications. Generally, theseengineered wood products require an initial finger jointing of shortpieces of wood or parallel laminated veneers (PLV) before they can beconstructed into long and/or thick beams or lumbers. Consequently, it isimportant that the finger-jointed area must have good strength to beused for structural wood applications. For present purposes, all of theforegoing products are known as “laminated wood products.”

At present, phenol-resorcinol-formaldehyde (PRF) is widely used inindustry for finger joint applications. When adhesive is applied to thefingers, the finger jointed wood or PLV is crowded together using an endpressure until a “tip gap” of 1-40 mils is achieved. Its is essentialthat the fingers do not “bottom out.” The finger joints then are movedinto a curing zone where hot platens or dielectric plates are used tocure the finger joints under heat or radio frequency and pressure fortypically less than 30 seconds and then the joints are removed away fromthe curing zone. The adhesives must be able to fill the gaps or voidsbetween the fingers when curing is complete in order for the product toexhibit good strength and a smooth appearance.

One the other hand, the speed of curing must be fast under theseconditions in order to hold the finger-jointed pieces together forfurther processing, such as beam lamination and I-joint assembly. Thisis especially true in a high-speed commercial finger jointing process.Generally, adhesives with high solids and fast curing profiles areregarded as appropriate for such an application.

It should be mentioned also that two-part PRF and melamine-formaldehyde(MF) adhesives generally are used in industry as adhesives inpreparation of radio frequency (RF) cured finger joint assemblies. Bothof these adhesives are highly polar, which makes them respond well to RFcuring. RF curing drives the bondline temperature sufficiently high topermit the MF or PRF to condense quickly. Due to the rigid ringstructure of both PRF and MF, these adhesives cure to give a high T_(g),rigid, three-dimensional network in a short time; thus, producingacceptable immediate handling strength (proof-loading).

Soy protein products have been utilized as adhesives for wood bondingsince the 1930's. Their use soon declined as a result of the developmentof petroleum derived adhesives. Economic and ecological pressures in the1990's renewed interest in the practical use of soy protein products inwood adhesives. Heretofore, soybean protein has been proposed for usewith phenolic resin, urea resin, or resorcinol resin, such as isdescribed in JP 06200226, 58034877, 50034632, and 04057881. In JP50034632 and 04057881, adhesives are proposed that consist of soyprotein as the major component and isocyanate as a minor componentbecause the soy protein, like wheat flour, is capable of thickening themixture by absorbing moisture in the wood to give an adhesive with fastdrying capability. In recent years, soybean-based adhesives weredeveloped and used primarily in a “honeymoon” system, such as thosedescribed by Scheid, “Finger-Jointing and Other Uses of EnvironmentallyFriendly Soy-Based Adhesives”, Wood Technology Clinic and Show,Conference Proceeding, Portland, Oreg., Mar. 25-27, 1998; and Steele, etal., “Finger Jointing Green Southern Yellow Pine With A Soy-BasedAdhesive”, Wood Technology Clinic and Show, Conference Proceeding,Portland, Oreg., March 25-27, 1998.

BRIEF SUMMARY OF THE INVENTION

An adhesive suitable for bonding wood is both heat curable and radiofrequency (RF) curable. This adhesive is composed of anisocyanate-terminated prepolymer and a hydrolyzed soy protein having apH of at least about 9. The weight ratio of prepolymer to soy proteinhydrolyzate ranges from about 70-90 to 30-10. Further increases in theratio of the soy protein hydrolyzate in the mix would lead to a highviscosity, paste-like material that would not be acceptable for most, ifnot all, applications contemplated herein, such as, for example, gluingwood, such as, for example finger joints.

DETAILED DESCRIPTION OF THE INVENTION

It is well known that woods are porous materials that contain differentmoisture contents, depending upon type of wood, storage environment,etc. Moisture contents can vary from as low as 5 wt-% to greater than 30wt-%. For adhesives to properly bond wood, it is important that theadhesive penetrates deep into the wood and interlock with the cellulosestructure upon cross-linking. If the adhesive cures too fast, however,such desirable penetration is not achieved. An adhesive predominatingwith soy protein hydrolyzate would react and dry very rapidly, thusdecreasing the ability of the adhesive to penetrate into the wood'sstructure to provide a strong bond.

To strike a balance, then an isocyanate-terminated prepolymer becomesthe predominant component of the adhesive composition and an aqueoushydrolyzed soy protein a minor component. Such a composition wouldsubstantially decrease the rapid thickening action of the soy proteincomponent, thus allowing the adhesive time to penetrate into the wood'sstructure. Water would react with the prepolymer for cure of theprepolymer in addition to the reaction between the prepolymer and thesoy protein hydrolyzate component. Such a balanced cure results instrong bonds by virtue of the wood penetration of the adhesive coupledwith the necessary speed of cure required in commercial settings. Theexamples will amply demonstrate the performance of the inventiveadhesive in engineered wood applications.

Information on soy protein can be found in, for example, Kirk-Othmer,Encyclopedia of Chemical Technology, Third Edition, Volume 21, pp.418-422 (1983). Soy protein hydrolyzates generally are prepared byhydrolyzing soy protein powder with an aqueous caustic solution.Treatment of soy protein with soluble caustic is necessary because thecaustic breaks the internal hydrogen bonds of the coiled proteinmolecules and makes most of their complex polar structure available foradhesion to wood. See, for example, Bian, et al., “Adhesive Performanceof Modified Soy Protein Polymers”, Polym. Prep., Am. Chem. Soc. Div.,Polym. Chem., Volume 39 (1988), pp. 72-73. The major mechanism ofprotein gluing involves the dispersing and unfolding of the proteinmolecules in solution so that the unfolded molecules' increased surfacearea can contact an increased area of the wood. Additionally, theunfolded protein molecules become entangled with each other during thecuring process for improving bond strength. The resulting proteinhydrolyzate generally has a pH of greater than about 9 and often betweenabout 9.5 and 12. Consequently, the hydrolyzed soy protein molecules arehigh in polarity, an added benefit for RF curing.

Appropriate caustics for use in hydrolyzing soy protein include, forexample, the oxides, hydroxides, and the like, of alkali metals andalkaline earth metals, caustic alcohols, and the like. Representativesuitable caustics include, for example, NaOH, CaO, CH₃ONa, C₂H₅ONa,C₃H₇ONa, and the like, and mixtures thereof. Non-caustic bases also canbe used including, for example, NH₄OH, various amine bases, and thelike. Reaction temperatures typically range from about 25° to about 120°C. with corresponding reaction times of about 1 to about 7 hours. Again,this operation is conventional and is known in the art.

Isocyanate-functional prepolymers are made from polyisocyanates reactedwith a compound containing active hydrogen functionality with hydroxylgroups being typical, although mercaptan groups, amine groups, andcarboxyl groups also can be used. Polyisocyanates are conventional innature and include, for example, hexamethylene diisocyanate, toluenediisocyanate (TDI), diphenylmethane diisocyanate (MDI), m- andp-phenylene diisocyanates, bitolylene diisocyanate, cyclohexanediisocyanate (CHDI), bis-(isocyanatomethyl)cyclohexane (H6XDI),dicyclohexylmethane diisocyanate (H₁₂MDI), dimer acid diisocyanate(DDI), trimethyl hexamethylene diisocyanate, lysine diisocyanate and itsmethyl ester, isophorone diisocyanate, methyl cyclohexane diisocyanate,1,5-napthalene diisocyanate, xylylene and xylene diisocyanate and methylderivatives thereof, polymethylene polyphenyl isocyanates,chlorophenylene-2,4-diisocyanate, polyphenylene diisocyanates availablecommercially as, for example, Mondur MR or Mondur MRS, isophoronediisocyanate (IPDI), hydrogenated methylene diphenyl isocyanate (HMDI),tetramethyl xylene diisocyanate (TMXDI), hexamethylene diisocyanate(HDI), or oligomer materials of these materials such as a trimer ofIPDI, HDI or a biuret of HDI, and the like and mixtures thereof.Triisocyanates and high-functional isocyanates also are well known andcan be used to advantage. Aromatic and aliphatic diisocyanates, forexample, (including biuret and isocyanurate derivatives) often areavailable as pre-formed commercial packages and can be used to advantagein the present invention.

Preferred polyols for reacting with the polyisocyanates include, forexample, polyether polyols (e.g., block polyethylene and polypropyleneoxide homo- and copolymers ranging in molecular weight from about 300 toabout 3,000) optionally alkylated (e.g., polytetramethylene etherglycols), caprolactone-based polyols, and the like. However, thecomponent also may be formulated with mixtures of aliphatic and aromaticpolyols, or a multi-functional, active hydrogen-bearing polymer. Thus,in addition to polyether polyols, the hydroxyl-functional component mayinclude derivatives of acrylates, esters, vinyls, castor oils, as wellas polymers and mixtures thereof.

Isocyanate equivalents should predominate over active hydrogenequivalents in the polyisocyanate/polyol reaction mixture in order forthe resulting prepolymer to contain residual isocyanate groups. Reactionconditions for this reaction are well known in the art, such asdescribed by Heiss, et al., “Influence of Acids and Bases on Preparationof Urethane Polymers”, Industrial and Engineering Chemistry, Vol. 51,No. 8, August 1959, pp. 929-934. Depending upon the reaction conditionsused (such as, for example, temperature and the presence of strong acidsor bases, and catalysts), the reaction may lead to the formation ofureas, allophanates, biurets, or isocyanates.

The isocyanate prepolymer must be separated from the aqueous hydrolyzedsoy protein in order to preclude premature gellation and crosslinking.This is because the isocyanate group from the prepolymer can react witheither water in the soy protein hydrolyzate solution or with any amineor any carboxyl group in the hydrolyzed soy protein molecules at arelatively fast rate of reaction, particularly under the influence ofcatalysis using dibutyl tin dilaurate catalyst (T-12 brand, seeExamples) and base (in the soy protein hydrolyzate). Thus, the inventivewood glue is a two-pack or two-part composition whose packs or parts aremixed together just prior to application to the wood.

Application of the inventive glue is conventional for this art. Cure ofthe glue can be by simple heating as taught in this art and practicedcommercially at, say, from about room temperature to about 175° C. fortimes ranging from as short as say, 30 seconds, on up to about 2minutes, with cure times dependent upon reaction temperature andcatalyst concentration.

Alternatively, radio frequency or dielectric heating can cure theinventive wood glue. The principal of dielectric heating is defined asthe rapid movement of the radio waves through a material that causesmolecular friction to take place and subsequently produce heat. Insteadof current flow, the forces used in dielectric heating are caused bycharges on the plates placed on opposite sides of the material to beheated—one plate being positive and one plate being negative. Theseoppositely charged plates set up forces of attraction betweenthemselves. The forces in the electric field can influence the movementof the adhesive molecules, because these molecules are not electricallysymmetrical, but have dipole moment, i.e., the measure of electricalasymmetry of a molecule. Since oppositely charged particles areattracted to each other, the molecules in the adhesive line up with thenegative poles towards the positive plate (or electrode) and thepositive poles towards the negative plate. As the charges on the platesreverse, the dipole molecules in the adhesive rotate to keep the samealignment just described. This rotation of the molecules producesfriction that generates heat that is required for cure of the adhesivecomposition. The amount of heat actually developed by the adhesivecomposition in the RF field depends upon factors including, for example,the amount of moisture in the composition, the strength (voltage) of theelectric field, the frequency of the radio waves, and the length of timethat the composition spends in the field.

Two important properties determine how much heat the adhesive materialwill develop in an alternating electric field: the dielectric constantand the power factor. The dielectric constant of a material is a measureof the ability of the dipole molecules in such material to rotate whensubjected to an electric field. The power factor of a material is ameasure of the ability of such material to convert the energy in theelectric field into heat energy. The dielectric constant is determinedby the strength of the permanent charge on the dipole molecules. Strongpermanent dipole charges increase the molecular movement. The linkagethat exists between the molecules of the material determines the powerfactor. These linkages hold the molecules closely together and theirresistance to movement results in friction when the molecules move and,thus, heat is generated.

Another factor that may contribute to heat in dielectric heating is theionic conductivity, given that some adhesives also contain ions. Someions in the adhesive composition are positively charged, while othersare negatively charged. When an adhesive composition is placed in analternating electric field set up between two positively charged plates,the negatively charged ions try to move toward the positive pole whilethe positively charged ions try to move toward the negative plate. Sincethe charge on the plates is rapidly reversing in dielectric heating,there is considerable back and forth movement of the ions which rapidchange in direction and movement results in frictional heating also.

Thus, for RF curability of the inventive adhesive or glue, it isimportant that the adhesive have sufficient polarity to respond to thedielectric or RF heating when it is placed in a dielectric heating unit.Since the immediate handling strength in the RF cured finger joint is animportant consideration, it is necessary that the adhesive shouldprovide a fast curing rate as well as a sufficiently high T_(g) that theadhesive will solidify rapidly in a short amount of time. While properselection of a catalyst may achieve the purpose of providing thenecessary rate of reaction for providing proof-loading (immediatehandling strength), they also contribute negative attributes to theadhesive, such as decreased open times, shelf stability, and the like.On the other hand, it is also important that the adhesive should possessa good water resistance, such as the requirements specified in the ASTMD-5751 non-structural laminate performance test and most specifically,the ASTM D-2559 structural laminate wet performance test. In this sense,the role of the soy protein hydrolyzate (the minor component) is tocontribute to the RF curability, and the role of the prepolymer (themajor component) is to provide the adhesive with integrity forstructural applications.

On the other hand, the soy protein hydrolyzate generally is prepared byhydrolyzing soy protein powder with aqueous caustic, as described above.Thus, the hydrolyzate typically has pH of above 9. Consequently, suchhydrolyzate is high in polar molecules which positively aids in RFcuring and may even contain a small amount of electrically conductivematerial. This makes the soy protein hydrolyzate an ideal component forinclusion in the adhesive composition of the present invention.

An important part of this invention is centered on the preparation of asoy protein hydrolyzate that will provide a glue mix (with theprepolymer) having an acceptable consistency and pot-life, because theprepolymer and soy protein hydrolyzate are incompatible and difficult tomix together due to the large difference of polarity between them. If asufficiently high shear rate is applied to force these two componentstogether, the resulting mix viscosity is too high to be acceptable forpractical (and commercial) application of the glue mix. Furthermore, thepresence of caustic in the soy protein hydrolyzate also catalyzes thecrosslinking reaction of the prepolymer and the soy protein hydrolyzatemix almost immediately, resulting in a mixed adhesive having anunacceptably short pot-life. Again, such an adhesive composition is notacceptable for commercial purposes.

Consequently, an appropriate inhibitor (such as, for example, benzoylchloride or monophenyldichlorophosphate) is added to the prepolymer toretard the crosslinking reaction of the mixed adhesive system. The gluemix consistency also is improved and the pot-life is increased to anacceptable range (e.g., say, 12-20 minutes) by incorporating a nonionicwetting agent (e.g., Dynol™ 604 surfactant) in the soy proteinhydrolyzate. On the other hand, there is a fine balancing point betweenthe glue mix pot-life and the immediate handling strength(proof-loading) after RF cure. Too long of a glue mix pot-life (say,greater than 20 minutes) usually results in undesirable proof-loadingfollowing RF cure because the rate of reaction has been decreased toomuch. Addition of these adjuvant components and others to adhesivecompositions, however, is well known and well practiced commercially,and such adjuvant components may be used in the inventive adhesive inconventional and unconventional fashion as those skilled in this artwill appreciate.

Finally, it should be noted that RF curing is self-limiting in terms ofheat generation. As the molecules in the composition cross-link orreact, the amount of free polar molecules decreases. With less polarmolecules to rapidly “vibrate” under the influence of RF, less heat isgenerated. Thus, over-heating generally is not a problem.

Equipment for RF curing is commercially available and well known in theart. Reference is made to the undated booklet entitled Radio FrequencyHeating, by Franklin International (Columbus, Ohio) for a good review ofthe fundamentals of RF heating and equipment used therein.

The following examples show how the present invention has been practicedbut should not be construed as limiting the invention. In thisapplication, all units are in the metric system unless otherwise noted.Also, all citations are expressly incorporated herein by reference.

EXAMPLES Example I

A 22-liter, three-neck round bottom reaction flask was charged with6,987 g of a polyether diol (MW of 2,000, average OH number of 56,viscosity @ 25° C. of 215 cps, density of 8.33 lbs/gal, Ashland ChemicalCo. code 033-192), 11,744 g of polymeric methylene diisocyanate or MDI(Mondur MRS poly(methylenephenylene) polyisocyanate, averagefunctionality of 2.8, average equivalent weight of 133, NCO content of31.6%, viscosity @ 25° C. of 250 cps, Miles Chemical) and 18.7 g ofD-1400 defoamer (polydimethylsiloxane and treated amorphous silica foamcontrol agent, Dow Coming Corporation, Midland, Mich.). Theseingredients were mechanically agitated at room temperature (viz., 24.8°C.) under a nitrogen blanket to form a mixture. 19.86 g of dibutyl tindilaurate catalyst (DABCO® T-12 catalyst, 18.0% total tin, Air Productsand Chemicals, Inc., Allentown, Pa.) was added to the mixture and a mildexotherm was observed to push the temperature to about 42° C. in 30minutes. A second portion of T-12 catalyst, 17.64 g, was added to thereaction flask and the reaction was continued for another 30 minutes.Finally, 140.6 g of benzoyl chloride was added to the reaction flask andmechanical agitation was continued to an additional 15 minutes toproduce an isocyanate prepolymer. This product was labeled as EP5815-106-3 or 5815-140.

Example II

The isocyanate prepolymer made in Example I was mixed with a soy proteinhydrolyzate (HTI ProBond 3050, 36-38% solids, pH of 9.5-11.0, viscosityof 400-2000 cps, Hopton Technologies, Inc., Albany, Oreg.) at varyingratios. Generally, the speed of the resulting reaction was based on suchratio (isocyanate prepolymer:soy protein hydrolyzate). When the ratio ofisocyanate prepolymer to soy protein hydrolyzate was e.g., 9:1), an opentime (time to cure) of greater than 10 minutes was observed. If thissame ratio was much lower (e.g., 3:2) the mixture cured to a granularsolid within 2 minutes. At a ratio of 4:1, an open time of 3-6 minuteswas observed to give an excellent finger joint performance.

Example III

The two-part adhesive composition disclosed in Example II (EP5815-106-3) was compounded at a 4:1 ratio, cured at either 330° F. or350° F., and used to bond parallel laminated veneer (PLV) finger joints.The following force and percent wood failure (WF) results were recorded:

TABLE 1 PRF EP 5815-106-3 EP 5815-106-3 (350° F.) (350° F.) (330° F.) 6HOURS 30 MINUTES 24 HOURS 1 HOUR 24 HOURS Force % Force % Force % Force% Force % Run (lbs) WF (lbs) WF (lbs) WF (lbs) WF (lbs) WF 1 9090 959310 95 12160 100 10110 100 11860 100 2 9900 90 11310 95 12270 100 8370100 8470 100 3 8280 90 10230 100 11330 100 9590 100 0790 99 4 8280 9012380 100 11050 100 8850 100 10710 100 5 7560 85 10960 100 12240 1009240 100 9830 100 6 9310 90 11110 100 11780 100 9130 95 8980 100 7 744995 10210 95 13090 100 8650 100 9500 99 8 7610 95 11610 100 14190 1009340 100 9570 100 9 6240 95 11000 95 10740 100 9070 100 11070 100 108990 90 9010 95 10930 100 10200 100 10760 100 11 10990 100 9970 95 11610100 10520 100 9780 100 12 9170 95 11770 95 10020 100 9250 100 10330 10013 10790 85 11840 95 12640 100 11750 100 9880 99 14 11320 95 9980 9511280 100 10440 100 12710 100 15 9940 100 10850 95 12140 100 11350 1009840 100 16 9710 85 10850 95 11230 100 10520 100 10050 100 17 9720 909350 100 9400 100 8720 100 9960 100 18 8350 85 11240 95 9540 99 8760 1007980 100 19 10230 90 8540 100 12290 100 9620 100 10670 100 20 10190 8511990 100 11420 99 9510 100 12090 100 21 9330 95 10020 95 10720 10010620 100 11870 99 22 8220 95 9350 95 11200 100 11190 100 12880 100 237090 90 10070 100 10160 99 9080 100 10820 100 24 8530 95 9980 100 11000100 10490 100 10610 100 25 10620 95 11350 100 11750 100 8010 100 11430100 26 9940 90 11540 100 11010 100 9580 100 10620 100 27 10030 90 10500100 11440 100 8050 100 10170 100 28 10000 95 12170 100 11220 100 11000100 12620 100 29 10400 90 10550 95 10360 100 11230 95 10950 100 30 1185090 10660 95 10360 100 11230 95 10950 100 31 10150 100 11070 100 1078-100 12780 99 32 9250 100 11760 100 11820 95 AVG 9311 92 10597 98 11350100 9952 100 10587 100 Std. (1325) (4) (987) (3) (1004) (1) (1252) (1)(1264 (1) Dev. # of 2 17 28 29 25 100% WF

These results demonstrate that the inventive adhesive not only providesexcellent finger joint application for PLV boards, but also outperformedthe industrial standard PRF composition.

Example IV

The two-part adhesive composition disclosed in Example II (5815-140) wascured at 330° F. for 30 seconds in a strength development study to joinDouglas fir finger joints with high moisture content (16%-22%). PRFadhesive was used as a comparison adhesive. The results recorded are setforth below.

TABLE 2* TIME EP 5815 140/HTI 3050 PRF (min) (psi) (psi)  5 4531 ± 675 3006 ± 957  10 5458 ± 1152 1782 ± 80  30 6018 ± 2969 4564 ± 1458 60 7408± 1790 3152 ± 1890 *Each data point is the average of 4 specimens.

These results demonstrate that the inventive adhesive provided fasterand stronger finger joint strength on high moisture content Douglas firwood than the industrial standard PRF.

Example V

Several formulations based on the commercial soy protein hydrolyzate,HTI 3050, and prepolymers containing different levels of the T-12 brandtin catalyst concentrations were compared in an engineered woodapplication using Douglas fir (specific gravity of 0.47-0.50) testprocedure followed was ASTM D-5751. The following results (PSI is poundsper square inch; WF is wood failure) were recorded.

TABLE 3 T-12 Catalyst Concentration 0* 0.05* 0.2** Closed Assembly Time(min) 8 6 4 Dry PSI 1963 1320 1505 WF (%) 95 85 95 Vacuum-Pressure PSI(Standard Deviation) 949 (101) 975 (94) 793 (127) WF (%) (StandardDeviation) 52 (17) 56 (13) 46 (24) Two-Cycle Boil PSI (StandardDeviation) 802 (113) 705 (87) 765 (56) WF (%) (Standard Deviation) 79(13) 85 (12) 69 (21) *Same formulation as in Example I, except in theT-12 concentration and the high reaction temperature (75 ± 5° C. for 3hours). **Same as in Example I.

These results demonstrate that the inventive adhesive formulations basedon soy protein hydrolyzates are suitable for non-structuralapplications.

Example VI

Two additional isocyanate prepolymers were made according to theprocedure set forth in Example I, except that an inhibitor was addedafter the NCO determination (ACC method Ac-21a-79) revealed that thedesired extent of reaction had been achieved.

TABLE 4 INGREDIENT* (g) 6204-144 6298-46A** Polyetherdiol (MW of 2,000,see Example I) 332.1 0 Polyether diol (MW of 1,000) 0 448 Mondur MRSpolyisocyanate (see Example I) 1116.9 1104 Rubinate 9310 polyisocyanate0 260.2 D-1400 antifoam agent (see Example I) 1.62 2.24 Dibutyl tindilaurate (T-12 brand, see 3.42 3.63 Example I)Monophenyldichlorophosphate (inhibitor) 4.05 4.54 *Polyether diol (MW of1000, OH number of 112, viscosity @ 25° C. of 322 cps, density of 8.34lbs/gal, Ashland Chemical Code 033-191). Rubinate 9310 polyisocyanate (%NCO = 29.3%, viscosity @ 25° C. = 35 cps, average functionality = 2.1,ICI Polyurethanes). **Same prepolymeras 6298-84B, 100A, 121C, 145C, and167.

It should be noted that the flexibility of the prepolymers can be rankedin the order of 5815-140>6204-144>6204-46A. It will subsequently bedetailed that, while the increased rigidity of the prepolymer structuremight help the immediate strength after RF curing, such prepolymer willnot have the necessary acceptable accelerated aging resistance to water(wet cycles under vacuum, pressure, or steam) to meet the standards forstructural (exterior) engineered wood applications.

Example VII

Several soy protein hydrolyzates were prepared at ambient temperatureaccording to the formulations set forth below.

TABLE 5 INGREDIENT (g) 6289-009A 6289-009B 6289-010B 6298-19B Deionizedwater 87.5 87.5 87.5 87.5 Pro-Cote 200 48.5 48.5 48.5 48.5 polymer*Soybean oil 1.5 1.5 1.5 1.5 Deionized water 72.5 72.5 72.5 72.5 Hydratedlime 6.0 6.0 6.0 6.0 (fresh)** Deionized water 12.0 12.0 12.0 12.0 50wt-% sodium 6.0 6.0 6.0 6.0 hydroxide 2-Phenyl phenol 2.5 2.5 2.5 2.5Sodium silicate 4.0 5.0 4.5 5.0 solution*** *Pro-Cote 200 naturalpolymer extract from soybeans (light tan granular powder, pH of 4.6 in awater slurry, less than 2% retained on 30 mesh screen, ProteinTechnologies International, St. Louis, MO). **prepared by mixing 6.6 gof anhydrous calcium oxide with 10 g of deionized water. ***SiO₂/Na₂Oweight ratio of 2.4 (Occidental Chemical Corp.)

A typical procedure can be found is Pizzi, Wood Adhesive-Chemistry andTechnology, Vol. 2, pp. 1-29 (1989) and involves mixing and dispersingsoy protein powder (Pro-Cote®200) and soybean oil in water at ambienttemperature for about 3 minutes. After the soy protein powder wasthoroughly dispersed, more water was added and mixing continued foranother 2 minutes. Hydrated lime then was added and mixing continued foranother 5 minutes, followed by the addition of NaOH (50 wt-%). Thisreaction was permitted to continue for about 30 minutes. The addition of2-phenyl phenol and sodium silicate solution was made to provide moldresistance in high humidity environments and to gain better viscositystability control.

Example VIII

Another technique was developed to prepare soy protein hydrolyzates at60° C. using the formulations set forth below.

TABLE 6 FORMULATIONS 6204- (g) INGREDIENT 112A 112B 112C 121 122A 122BWater 688 658 688 592 685 688 Soy Protein Powder (Pro-Cote 194 194 194174.6 0 0 200) Soy Protein Powder (Pro-Cote 0 0 0 0 194 194 PX-270)*2-Phenyl phenol 10 10 10 9 10 10 Antifoam (Dow Corning 1400 0.4 0.4 0.40.4 0.4 0.4 agent) NH₄OH (37 wt-%) 24.1 24.1 24.1 0 0 0 NaOH (50 wt-%) 012.1 30.1 19.2 15.5 15.5 CaO (98% purity) 0 0 0 7.1 12.5 18.8 Water (toadjust viscosity) 124 124 124 27 62.5 62.5 Sodium silicate solution 0 00 37 0 0 (SiO₂/Na₂O ratio of 2.4) *Pro-Cote PX-270 is a modified polymerderived from soybeans (fine light tan powder less than 2% retained on 30mesh screen, pH of 4.7 in water slurry, Protein TechnologiesInternational, St. Louis, MO).

TABLE 7 FORMULATIONS 6298- (g) INGREDIENT 139B 139C 142B 156B 162B Water324 324 482 500 366 Soy Protein Powder 97 97 97 97 97 (Pro-Cote 200)2-Phenyl phenol 5 5 5 5 5 NaOH (50 wt-%) 10.67 10.67 3.2 3.2 10.67 CaO(98% purity) 3.95 3.95 0.79 0.79 3.95 HCl (4.63 wt-%) 94.46 122 0 094.46 NaCl 0 0 6.66 6.22 0 Dynol ™ 604 surfactant 0 0 0 1.02 1.59 Sodiumsilicate solution 20.4 19.55 19.55 19.55 20.4 (SiO₂/Na₂O ratio of 2.4)

Water and 2-phenyl phenol were charged into a round-bottomed reactor andheated to 60°±2° C. with mechanical agitation. When the temperaturereached 60°±2° C., soy protein powder was added to the reaction withstirring continued for 2-5 minutes until a homogeneous dispersion wasachieved. A 50 wt-% aqueous NaOH solution and/or NH₄OH and/or CaO and/orsodium silicate and/or HCl and/or NaCl and/or water and/or Dynol™ 604solution then was/were slowly added into the reaction to adjust thefinal pH and viscosity.

Example IX

Two-part polyurethane adhesives were made from the isocyanateprepolymers of Example I and the soybean hydrolyzates of Examples VII(Tables 5) at a ratio weight of 4:1 in order to obtain a homogeneousglue mixture. The glue mixture along with a commercial melamineformaldehyde adhesive was applied to Douglas fir finger joint specimens(1.5″×1.5″×6″). The joints then were crowded together by a hammer untila “tip gap” of 1-40 mils was achieved prior to curing by RF. FollowingRF curing, the surface temperature of the joints was measured and theadhesives were ranked visually within 20 seconds of RF treatment as:wet, tacky, or dry. Following RF curing, the bondline temperature of thejoints also was measured and the finger joint strength was determined byclamping the finger joints into a vise and hitting them with a hammerwithin 30 seconds. A subjective ranking was assigned depending on therelative resistance of the finger joint to breaking under the impact ofthe hammer swing as: poor, fair, good, or excellent.

Curing of the finger joints was accomplished using low, 5 MHz RF (4,200v, 30 seconds) curing. The results recorded are set forth below.

TABLE 8 Bondline Temp. Hammer L Adhesive (° F.) Strength Prepolymer ofExample I/6298-19B 140 Excellent hydrolyzate of Example VII, Table 5(4/1 weight ratio) Cascomel ® MF 216S melamine 177 Excellentformaldehyde adhesive (Borden Chemicals, Columbus OH)

These results demonstrate that at the correct bondline temperature, theinventive adhesive formulation provided excellent adhesive performance.Such performance matched that of a conventional commercial melamineformaldehyde adhesive.

Example X

Adhesive formulations like those described in Example IX were preparedusing different soy protein hydrolyzates (see Example VIII, Table 6)having varying pH levels and the isocyanate prepolymer 6298-84B (seeExample VI, Table 4). The finger joints were cured at 30 MHz (3,500 v,10 seconds). Following RF curing, the surface temperature of the jointswas measured and the adhesives ranked visually within 20 seconds of RFtreatment as: wet, tacky, or dry. Bond strength was determined byclamping the finger joints into a vise and hitting them with a hammer at30 seconds. A subjective ranking was assigned depending on theresistance of the finger joint to breaking under the impact of thehammer swing as: poor, fair, good, or excellent. The results recordedare set forth below.

TABLE 9 Soy Protein Surface Temp Appearance Bond Hydrolyzate* pH AfterRF (° F.) After RF After RF 6204-112A 9.5 128 Tacky Good 6204-112B 10.2130 Tacky Fair 6204-112C 11.9 135 Dry Good *See Example VIII, Table 6.

These results demonstrate that as the pH of the soy protein hydrolyzatesincrease, the degree of RF curing increases based on measured surfacetemperature, ranked appearance, and bond performance. This data alsowould suggest that as pH increases, the polarity of the mixed adhesiveincreases, which leads to a better RF cure.

Example XI

Tests like those described in Example X were conducted on prepolymer6298-121C (Example VI, Table 4) and the soy protein hydrolyzate ofExample VIII, Table 7. The results recorded are set forth below.

TABLE 10 Soy Protein Time of Test Surface Temp. Hammer Hydrolyzate pHPost RF (sec) Appearance (° F.) Strength Amp. Draw* 6204-133B 10.8 15Dry 133 Good 0.65 20 Dry 126 Excellent 0.75 20 Dry 147 Excellent 0.65 30Dry 145 Excellent 0.70 30 Dry 144 Good 0.60 40 Dry 145 Excellent 0.75 40Dry 144 Excellent 0.60 6204-135 9.5 20 Tacky 130 Good 0.70 20 Tacky 150Poor 0.65 30 Tacky 162 Fair 0.70 30 Tacky 142 Fair 0.60 40 Dry 140Excellent 0.75 40 Dry 145 Excellent 0.70 6204-137 10.7 15 Dry 153 Good0.70 20 Dry 145 Excellent 0.75 20 Dry 145 Excellent 0.75 30 Dry 160Excellent 0.85 30 Dry 145 Excellent 0.70 40 Dry 172 Excellent 0.70 40Dry 150 Excellent 0.70 6204-139 10.2 20 Tacky 156 Poor 0.65 20 Tacky 145Fair 0.65 30 Dry 148 Good 0.75 30 Dry 150 Excellent 0.70 40 Dry 149Excellent 0.70 40 Dry 160 Excellent 0.68 *Amp Draw is the peak amperagedraw during RF curing

These results demonstrate that all of the polyurethane-soy proteinhydrolyzate adhesives cured well by RF, based on the draw of currentduring RF treatment, the measured surface temperatures, and theappearances after RF curing. Most importantly, these formulationsprovided excellent hammer strength when tested at 15, 20, 30, and 40seconds after RF cure. Such results are indicative that the RF curedfinger joints would have an acceptable immediate handling strength also.Among the formulations tested, soy protein hydrolyzate 6204-137 wasjudged the best.

Example XII

While RF curability is an important consideration in the development oftwo-part polyurethane-soy protein hydrolyzate adhesives, the ultimatestrength of the finger joint is an equally important consideration.Thus, finger joint specimens were prepared by first cutting each pairedspecimen member into 1.5″×1.5″×6″ segments to be cured by RF (30 MHz,3500 v, 10 seconds). After the curing of the mated finger joints, eachspecimen then was cut into 1″×⅜×11″ specimens to be tested at specifictimes post RF cure. The results displayed below are based on prepolymer6298-100A (see Example VI, Table 4) mix with soy protein hydrolyzates ata 4:1 ratio.

TABLE 11 One Day (Average 4 Days (Average of 5 Specimens) of 10Specimens) Soy Protein Strength Strength Hydrolyzate* (psi) WF % (psi)WF % 6204-121 5312 ±, 1816 88 ± 12 5744 ± 1137 92 ± 6  6204-122A 6348 ±2202 84 ± 15 7226 ± 2082 81 ± 21 6204-122B 6755 ± 1429 82 ± 19 7284 ±806  81 ± 19 *For hydrolyzates, see Example VIII, Table 6.

TABLE 12* Soy Protein Hydrolyzates* 6298-139C 6298-142B Appearance DryDry Peak Amperage Draw 0.75 0.73 Hammer Strength Excellent ExcellentUltimate Strength (psi)** 6959 ± 1387 5321 ± 1288 % Wood Failure 47 ± 2542 ± 34 *For Hydrolyzes, see Example VIII, Table 7; and for prepolymer,see 6298-145C in Example VI, Table 4. Prepolymer:Soy Protein Hydrolyzateof 4:1. **Ultimate Strength is an average of 9 specimens RF cured, andthen aged at ambient temperature for 6 days.

These results demonstrate that the two-part polyurethane-soy proteinhydrolyzate adhesives possess good ultimate finger strength when curedby RF.

Example XIII

Additional RF curing was conducted using the three prepolymers describedin Examples I and VI, and with the soy protein hydrolyzates described inExample VIII, Table 7. Bond strength (hammer strength) was tested 30seconds after RF cure.

TABLE 13 Time of Test Surface Prepolymer (mix ratio with soy RankedPot-Life Post RF Cure Temp. Hammer Amp. Draw protein hydrolyzate) (min)(min) Appearance (° F.) Strength (Peak-End) 6298-156B SOY PROTEINHYDROLYZATE 6298-167 (80/20) 22 30 Dry 138 Good 0.60-0.50 6298-167(75/25) 13 30 Dry 151 Excellent 0.75-0.55 6204-144 (80/20) 16.5 30 Dry140 Excellent 0.65-0.50 8364A37174 (80/20)* 9.5 20 Dry 149 Excellent0.70-0.55 8364A37174 (80/20) 9.5 30 Dry 140 Excellent 0.65-0.508364A37174 (75/25) 8.5 30 Tacky 151 Poor 0.80-0.60 6298-162B SOY PROTEINHYDROLYZATE 6298-167 (80/20) 9.5 30 Dry 142 Excellent 0.60-0.50 6204-144(80/20) 8 30 Dry 156 Excellent 0.70-0.55 8364A37174 (80/20) 7.5 30 Dry150 Excellent 0.70-0.60 8364A37174 (75125) 3.5 30 Dry 143 Excellent1.05-0.55 *8364A37174 prepolymer is the same as 5815-140 of Example I.

TABLE 14 Prepolymer (mix ratio with soy Time of Test Surface ProteinRanked Pot-Life Post RF Cure Temp. Hammer Amp. Draw hydrolyzate) (min)(min) Appearance (° F.) Strength (Peak-End) 6298-162B SOY PROTEINHYDROLYZATE 6298-167M (80/20)* 24 30 Tacky 148 Fair 0.65-0.55 6298-167M(80/20) 24 45 Tacky 150 Fair 0.75-0.60 6298-167M (80/20) 24 60 Tacky 158Good 0.70-0.55 6204-167M (80/20) 17 30 Tacky 123 Poor 0.65-0.556204-167M (80/20) 17 45 Tacky 138 Poor 0.65-0.55 8364A37174M (80/20)18.5 30 Tacky 148 Excellent 0.65-0.55 8364A37174M (80/20) 18.5 45 Tacky141 Poor 0.70-0.55 6298-167M (75/25) 4 30 Dry 144 Excellent 1.15-0.556204-144M (75125) 5 30 Dry 130 Excellent 1.20-0.60 *The “M” series ofprepolymers contained an additional 0.25% ofmonophenyldichlorophosphate.

These results indicate that as the prepolymer and soy proteinhydrolyzate mix ratio decreased from 4:1 to 3:1, the cured adhesiveappeared dry, together with excellent hammer strength. However, thepot-life became short. On the other hand, if an additional 0.25%inhibitor (monophenyldichlorophosphate) is added to the prepolymer, theranked pot-life increased. This substantially retarded the RF curingwhich led to a tacky appearance and decreased bond strength.

Example XIV

Finger joint ultimate strength also was obtained using the threeprepolymers described in Example I and VI, and the soy proteinhydrolyzates described in Example VIII, Table 7. The finger jointspecimens were cured by RF (30 MHz, 3500 v, 10 seconds). After standingat ambient temperature for 7 days, these specimens were cut into1″×⅜″×11″ specimens to be tested for tensile strength. The resultsrecorded are displayed below:

TABLE 15 Wood Strength, psi (Wood Failure, %) 6298-167/ 6298-167/6204-144/ *8364A37174/ 6204-144/ 8364A37174/ Sample 6298-156B 6298-156B6298-156B 6298-156B 6298-162B 6298-156B No. (4/1) (3/1) (4/1) (4/1)(4/1) (4/1) 1 4651 (20) 7947 (45) 5616 (99) 5029 (99) 9973 (98) 6517(99) 2 5288 (70) 8779 (30) 6331 (99) 5571 (99) 8016 (90) 7821 (99) 34192 (20) 5165 (40) 7707 (99) 6291 (98) 9328 (95) 5656 (99) 4 5632 (80)7253 (90) 7152 (30) 5398 (100) 8237 (40) 3584 (100) 5 5072 (900 8987(90) 7376 (30) 5656 (100) 8509 (45) 3680 (100) 6 7555 (85) 8165 (100)8445 (40) 6616 (99) 7971 (100) 2904 (100) 7 6539 (40) 3915 (100) 4901(99) 3381 (99) 7123 (99) 8053 (90) 8 8187 (25) 4899 (100) 6085 (95) 4371(100) 8173 (90) 5091 (99) 9 6328 (25) 6963 (70) 6736 (90) 4936 (99) 8995998) 7061 (95) Average 5938 (51) 6898 (74) 6705 (76) 5249 (99) 8481 (84)5586 (99) St. Dev. 1330 (30) 1826 (28) 1098 (32) 978 (1) 843 (24) 1911(3) *8364A37174 is the same as 5815-140 prepolymer.

These results demonstrate that adhesives derived from prepolymers6204-144 and 8364A37174 exhibited better overall ultimate finger jointstrength than the adhesive derived from the 6298-167 prepolymer, takingboth strength and wood failure into consideration.

Example XV

In order to determine whether the two-part polyurethane-soy proteinhydrolyzate adhesives exhibit good accelerated aging (wet stress)resistance, ASTM D-5751 non-structural laminate and ASTM D-2559structural laminate wet performance tests were performed. Prepolymersdescribed in Examples I and VII were mixed with different soy proteinhydrolyzates at a weight ratio of 4:1. The results recorded are setforth below.

TABLE 16 ASTM D-5751 Douglas Fir (MC of 6.5-7.2%, Sp. Gr. Of 0.41-0.51)Prepolymer 8364A37174* 6298-145C** 8364A37174 6298-145C Hydrolzate6298-156B** 6298-156B 6298-156B 6298-156B CAT (min)  13  12   7   6 Dry(psi) 1656 1327 1456 1336 Dry (WF %)  85  50  90  75 Vac-Pressure (psi)881 ± 34  422 ± 251 886 ± 54  358 ± 317 Vac Pressure (WF %) 81 ± 16 9 ±9 81 ± 12 358 ± 317 2-Boil Cycles (psi) 712 ± 80  451 ± 321 791 ± 66 510 ± 254 2-Boil Cycles (WF %) 65 ± 17 44 ± 20 80 ± 13 54 ± 28*8364A37174 is the same as 5815-140 of Example I. **For 6298-145C, seeExample VI, Table 4. ***For 6298-156B, see Example VIII, Table 7.

TABLE 17 ASTM D-2559 Douglas Fir (MC of 6.9-8.2%, Sp. Gr. OF 0.46-0.486298-145C* 6298-145C 8364A37174** 8364A37174 Adhesive 6298-156B***6298-162B*** 6298-156B 6298-162B SPECIFIC GRAVITY OF BOARD Board 1 0.4450.445 0.444 0.444 Board 2 0.464 0.460 0.459 0.457 Board 3 0.538 0.5330.478 0.472 Board 4 0.465 0.465 0.470 0.472 Board 5 0.445 0.448 0.4540.454 Board 6 0.439 0.441 0.441 0.441 DELAMINATION % PER GLUELINE GL110.81 5.22 0.56 0.31 GL2 20.00 6.46 0.15 0.27 GL3 5.97 8.02 0.43 0.35GL4 16.38 8.52 0.79 0.14 GL5 4.66 7.05 0 2.41 TOTAL 57.82 35.27 1.933.48 DELAMINATION (%) *For 6298-145C, see Example VI, Table 4.**8364A37174 is the same as 5815-140 of Example I. ***For 6298-156B or162B, see Example VIII, Table 7.

The foregoing tabulated results clearly indicate that the adhesivederived from the flexible prepolymer, 8364A37174, outperformed theadhesive derived from the rigid polymer system, 6298-145C, in the wetstress performance tests using soy protein hydrolyzates 6298-156B and6298-162B using different closed assembly times.

Example XVI

Additional testing according to ASTM D-2559 delamination specificationsof the 4:1 weight ratio prepolymer:soy protein was undertaken with thefollowing results being recorded.

TABLE 18 Douglas Fir (MC of 8-10%, Sp. Gr. Of 0.45-0.53) Adhesive5815-140* 5815-140** 5815-140** 6289-009A*** 6289-009B*** 6389-010B***Closed Assembly 6 6 4 Time (min) SPECIFIC GRAVITY OF BOARDS Board 10.493 0.476 0.477 Board 2 0.446 0.481 0.481 Board 3 0.491 0.550 0.558Board 4 0.447 0.519 0.519 Board 5 0.485 0.486 0.487 Board 6 0.447 0.4640.462 DELAMINATION % PER GLUELINE GL 1 2.36 0 0.38 GL 2 1.60 0.36 1.03GL 3 1.30 1.30 4.29 GL 4 0.55 1.53 3.59 GL 6 3.48 0.48 1.27 TotalDelamination % 9.29 3.67 10.56  *Same as EP 5815-106-3, see Example I.**Same as EP 5815-106-3 except without tin catalyst from Example I.***6289 series, see Example VI, Table 5.

TABLE 19 Soy Protein Hydrolyzate: 6298-174 (same as 6298-156B) DouglasFir (MC of 7-10%, Sp. Gr. Of 0.050-0.60) Prepolymer Used 6204-144*8364A37174** 6204-144 8364A37174 Closed Assembly 10 9 5 4 Time (min)SPECIFIC GRAVITY OF BOARD Board 1 0.507 0.508 0.514 0.536 Board 2 0.5220.517 0.511 0.529 Board 3 0.552 0.574 0.582 0.596 Board 4 0.536 0.5340.530 0.529 Board 5 0.522 0.523 0.525 0.509 Board 6 0.507 0.504 0.5010.500 DELAMINATION % PER GLUELINE Glueline 1 0 0 0.56 0.94 Glueline 20.07 0 0.13 0 Glueline 3 0 0.09 0.07 0.08 Glueline 4 0 0 0 0 Glueline 50 2.22 0 0 Total 0.07 2.3 0.76 1.01 Delamination % *For 6204-144, seeExample VI, Table 4. **8364A37174 is the same as 5815-140 of Example I.

These results indicate that low degrees of delamination were obtainedwith the novel adhesive, which in turn indicates its suitability forexterior structural engineered wood applications, particularly with themore flexible prepolymers 8364A37174 and 6204-144.

What is claimed is:
 1. A laminated wood product adhesively joined withthe cured residue of an adhesive which comprises: (a) anisocyanate-terminated prepolymer; and (b) aqueous hydrolyzed soy proteinhaving a pH of at least about 9, the weight ratio of (a) to (b) rangingfrom about 70:30 to 90:10.
 2. The laminated wood product of claim 1,wherein said adhesive has been cured by heat or radio frequency (RF)curing.
 3. The laminated wood product of claim 1, wherein saidisocyanate-terminated prepolymer is made from an isocyanate componentselected from hexamethylene diisocyanate, toluene diisocyanate (TDI),diphenylmethane diisocyanate (MDI), m- and p-phenylene diisocyanates,bitolylene diisocyanate, cyclohexane diisocyanate (CHDI),bis-(isocyanatornethyl)cyclohexane (H₆XDI), dicyclohexylmethanediisocyanate (H₁₂MDI), dimer acid diisocyanate (DDI), trimethylhexamethylene diisocyanate, lysine diisocyanate or its methyl ester,isophorone diisocyanate, methyl cyclohexane diisocyanate, 1,5-napthalenediisocyanate, xylylene diisocyanate or xylene diisocyanate or methylderivatives thereof, polymethylene polyphenyl isocyanates,chlorophenylene-2,4-diisocyanate, polyphenylene diisocyanates,isophorone diisocyanate (IPDI), hydrogenated methylene diphenylisocyanate (HMDI), tetramethyl xylene diisocyanate (TMXDI),hexamethylene diisocyanate (HDI), or oligomers thereof, or mixturesthereof.
 4. The laminated wood product of claim 1, wherein saidisocyanate-terminated prepolymer is made from a component containing anactive hydrogen group.
 5. The laminated wood product of claim 4, whereinsaid active hydrogen group component is selected from an acrylate group,an ester group, a vinyl group, a castor oil, or polymers or mixturesthereof containing active hydrogen groups.
 6. The laminated wood productof claim 5, wherein said active hydrogen group component is selectedfrom aliphatic or aromatic polyether polyols optionally alkylated, orcaprolactone-based polyols.
 7. The laminated wood product of claim 1,wherein said isocyanate pre-polymer has an NCO content of between about17 and
 22. 8. The laminated wood product of claim 1, wherein saidaqueous hydrolyzed soy protein has a pH ranging from between about 9 and11.5.